This program of research is designed to determine the influence of the diet on brain functions thought to be controlled in part by serotonin-containing brain neurons. It also explores the effects of the diet on other chemical parameters of brain, including amino acids and other monoamine neurotransmitters. Specifically, the work in progress concerns: (1) the effect of diet-induced changes in brain serotonin on growth hormone secretion: (2) the effect of high-protein diets on brain serotonin levels and synthesis; (3) the effect of meal ingestion on the brain levels of dopamine and norepinephrine: (4) The effect of single meals on the brain levels of each of the large neutral amino acids; and (5) the relationship between serotonergic neurons and pain sensitivity, and the effects of diet on pain sensitivity. The results of these studies should help to elucidate the functional consequences and significance to the body of having a set of brain neurons (i.e., those containing serotonin) whose transmitter levels are tied to peripheral metabolic state.